Log periodic structure feed system



March 3, 1964 F. G. ARNOLD ETAL LOG PERIODIC STRUCTURE FEED SYSTEM Filed Feb. 23, 1962 5 Sheets-Sheet 1 INVENTORS FRED R. ORE FORREST 6. ARNOLD March 3, 1964 F. G. ARNOLD ETAL 3,123,327

LOG PERIODIC STRUCTURE FEED SYSTEM Filed Feb. 25, 1962 v 5 Sheets-Sheet 2 I00 X H6 3 IN ENTORS FRED R. 0195 FORREST G. ARNOLD BY F. G. ARNOLD ETAL 3,123,827

LOG PERIODIC STRUCTURE FEED SYSTEM March 3, 1964 5 Sheets-Sheet 3 Filed Feb. 25, 1962 INVENTORS FRED R. ORE FORREST 6. ARNOLD ATTORNEYS March 3, 1964 F. G. ARNOLD ETAL 3,123,827

LOG PERIODIC STRUCTURE FEED SYSTEM Filed Feb. 25, 1962 5 Sheets-Sheet 4 IN V EN TORS FRED R'ORE FORREST 6. ARNOLD MMM I A 7' TOR/VEYS March 3, 1964 F. G. ARNOLD ETAL LOG PERIODIC STRUCTURE FEED SYSTEM 5 Sheets-Sheet 5 Filed Feb. 23, 1962 COAX FEED ELI-5545 l l 1 l l INVENTORS FRED R. ORE BY FORREST G. ARNOLD A TTORNE rs United States Patent 3,123,827 LOG PERIODIC STRUCTURE FEED SYSTEM Forrest G. Arnold, Cedar Rapids, Iowa, andFred R. Ore, Champaign, 11., assignors to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Filed Feb. 23, 1962, Ser. No. 174,969 8 Ciaims. (Cl. 343-7925) This invention relates generally to log periodic antenna structures and, more particularly, to an improved means of feeding the input signal to logarithmic periodic antenna structures (hereinafter sometimes referred to as log periodic antennas) whereby the construction of the antenna structures is simplified.

In the introduction of the specification a log periodic antenna element will first be defined generally, with reference to co-pending applications and issued patents for a more detailed description thereof.

Next, it will be shown that one of the difficulties of present log periodic antenna structures lies in their large size with attendant structural problems due to wind, snow, and sleet. Such structural problems run the cost of some types of log periodic antennas into many thousands of dollars. Consequently, in the body of the specification it will be shown how the present improvement in feeding an input signal to this antenna has resulted in simplification of the antenna structure with a resultant lowering of cost.

Logarithmic periodic antennas are a fairly recent development in the antenna art. Perhaps the most important feature of the log periodic antennas lies in their ability to maintain a constant radiation pattern and a constant impedance over large frequency changes on the order of 10 or to l, or even greater. Such log periodic antenna systems may be described generally as consisting of a plurality of individual antenna elements, each antenna element being generally triangular in shape, having a vertex, and being confined within an angle on extending from a vertex. A boom of conductive material is positioned along the bisector of the angle oz and functions to supply electrical signals to the antenna elements, as Well as to support said elements. Each antenna element is comprised of at least two radial sections, each section being generally triangular in shape with a common vertex and a common side, said common side being the boom referred to above. The outer side of each triangularly shaped radial section is defined by a radial line extending from the vertex at an angle 04/ 2 formed with respect to said center line or boom of the antenna element. Further, each radial section has a plurality of teeth comprised of elements which extend outwardly in a generally transverse manner with respect to the center line of the antenna element. Such teeth are all similar to one another in shape, but become progressively larger and spaced progressively farther apart as the distance from the vertex increases. The above-mentioned size and spacing relationships of the teeth may be expressed by stating that in a given radial section the radial distance from the vertex to a given point on any given tooth bears a constant ratio T to the radial distance to a corresponding point in the adjacent tooth next farthest removed from the vertex than said given tooth. In the most general case, where each antenna element employs two radial sections lying in the same plane, the teeth of one of the radial sections are positioned opposite the gaps between the teeth of the other radial section. It is to be noted that throughout this specification a single tooth of an antenna radial section will sometimes be referred to as a monopole.

The log periodic antenna elements described in the preceding paragraphs may be alranged in many different combinations to perform desired functions. Usually, an-

3,123,827 Patented Mar. 3, 1964 "ice tenna elements are employed in multiples of two, i.e., in pairs. For example, a pair of log periodic antenna ele ments may be arranged in such a manner that the vertices are near each other (but not quite touching), and the bodies of the antennas would be positioned with respect to each other as opposite sides of a pyramid. Such an arrangement is known in the art as a nonplanar array of log periodic antenna elements. For a more detailed description of such structure, the readers attention is directed to the following patent applications which are hereby incorporated by reference into the present specification: United States patent application Serial No. 721,408, filed March 14, 1958, by Raymond H. Du Hamel and Fred R. Ore, and entitled Logarithmically Periodic Antenna, now Patent No. 3,079,602; United States patent application Serial No. 804,357, filed April 6, 1959, by Raymond H. Du Hamel and David G. Berry, entitled Unidirectional Frequency Independent Coplanar Antenna, now Patent No. 2,989,749; United States patentapplication Serial No. 841,391, filed September 21, 1959, by Raymond H. Du Hamel et al., entitled Antenna Arrays, now Patent No. 3,059,234; United States patent application Serial No. 841,400, filed September 21, 1959, by Raymond H. Du Hamel et a1, entitled Broadside Antenna Arrays, now Patent No. 2,984,835; United States patent application Serial No. 31,068, filed May 23, 1960, by David G. Berry entitled Unidirectional Circularly Polarized Antenna.

It has. been found that the cost of the antenna arrays described in the preceding paragraphs, and in the applications incorporated herein by reference, has been quite high, especially in the case of structures designed for the low frequency portion of the spectrum. Such high cost is due primarily to the fact that many log periodic antenna arrays require a number of large antenna elements which are mounted on large masts many feet above the ground. Structural difficulties are encountered in that the antenna elements usually consist of rather long dipole elements mounted on central booms. In the presence of wind or sleet the dipole elements function as cantilever levers and provide rather serious stresses and strains at the point of connection to the boom elements. Structure to compensate for these stresses and strains is expensive.

One method that has been employed to simplify the construction of a log periodic antenna array is disclosed in co-pending United States patent application Serial No. 113,700, filed May 31, 1961, by David G. Berry, entitled Vertically Polarized Unidirectional Log Periodic Antenna Over Ground, and incorporated by reference herein. In this structure a single antenna element has two radial sections mounted at right angles to each other on a common boomwhich is positioned so that the boom is parallel with, and just a small distance above, a reflecting surface, such as the surface of the earth. The monopoles making up one of the radial sections are positioned vertically with respect to the reflecting surface and functions as the radiating section to produce a vertically polarized electric field. The monopoles forming the second radial section are positioned parallel with respect to the ground surface and, because of their cooperation with their im ages produced in the reflecting surfaces, function as sections of transmission lines instead of radiating elements. More specifically, the monopoles (or stubs) forming the second radial section will function as loading elements along the boom; said loading being a necessary requisite to radiation from the vertically positioned monopoles.

In another form of the prior art the stubs may be replaced by other structures which will perform the same loading function such as, for example, a resonator.

One of the difiiculties presented by the structure described above lies in the fact that the boom must be electrically isolated from ground potential. To overcome this difiiculty involves the use of some rather large and expensive insulators which add to construction problems. A further difiiculty of the structure just described is the fact that the power-handling capabilities are lower than desired in some applications.

The principal object of the present invention is to provide input signal feed-in means which will have large power-handling capabilities and which will eliminate many structural difficulties found in present log periodic antenna structures.

A further object of the invention is to provide a log periodic antenna structure consisting of a single radial section in which the central boom may be mounted directly on the ground plane, thus reducing the cost and difiicultness of installation.

A third object of the invention is a means for feeding the input signal to a log periodic antenna element in such a manner that one radial section thereof will feed against the other radial section thereof to form a complete antenna system, with the teeth of both radial sections being securely fastened to a common boom, thus providing a structure of great structural strength.

A fourth purpose of the invention is the improvement of means for feeding an input signal to a log periodic antenna system.

A fifth object of the invention is the improvement of log periodic structures, generally.

In accordance with the invention, the antenna structure is comprised of at least two radial sections lying in the same plane and securely connected to a common boom which is positioned along the center line of the antenna element. On either side of the common boom, that is to say, in each radial section there is provided a coaxial type signal feeding (or feed-in) structure which lies in a line intercepting the vertex of the radial section and, further, which is afiixed to each of the teeth in the radial section. More specifically, each of the teeth is comprised of a first section which is secured rigidly at one end to the common boom and which has its outer edge defined by the angle a. The coaxial type feed structure is supported by the teeth.

The coaxial feed means is comprised of an inner conductor and an outer conductor with the outer conductor being separated or broken at each interval between teeth; each separation occurring near the midpoint of the section of the coaxial feeding structure between any two adjacent teeth. An input signal feed-in coaxial cable, which is distinct from the coaxial feeding structures, is passed through one of the coaxial feeding structures from the rear of a first radial section and forms the inner conductor of said coaxial feeding means; but does not make electrical contact therewith. Said coaxial feed-in cable is brought through to the vertex of the antenna element while the outer conductor is terminated near said vertex but with no direct connection to any other element. The inner conductor of the feed-in coaxial cable is connected to the inner conductor of the coaxial feeding means of the second radial section.

In accordance with another form of the invention only one real radial section is required. Said real radial section is mounted directly on a grounded surface such as a horizontally positioned copper screen and in a plane vertical to said grounded screen. A reflection of the radial section is then formed in the grounded screen which is a mirror image of the real radial section, thus providing a complete antenna system having two radial sections which feed against each other. The coaxial feed-in cable is brought up under ground with the outer sheath being directly connected to the grounded screen and the inner conductor being connected to the inner conductor of the coaxial feeding means of the real radial section.

In accordance with a third form of the invention, two similar antenna elements each comprised of two radial sections, as described above, can be arranged in a single plane with the vertices of the two antenna elements pointing at each other and substantially coincident in space. A common boom runs through the two antenna elements, which boom can then be mounted perpendicularly to the grounded plane so that a horizontally polarized bidirectional radiation pattern is created.

In accordance with still another form of the invention a second pair of antenna elements positioned in a single plane with their vertices pointing towards each other are afiixed on the same boom as the first two elements, in such a manner that the four vertices of the four antenna elements coincide substantially and the plane of the first pair of elements is substanitally normal to the plane of the second pair of elements. By stretching or shrinking one pair of elements with respect to the other by a factor T14 a rotating omnidirectional radiation pattern is obtained. As will be discussed in the specification in more detail later, the means of feeding in the signal, as described in connection with the embodiments generally set forth above, can be adapted to other type structures which are capable of generating radiation patterns other than these already mentioned.

It is to be noted that one of the principal features of the invention lies in the fact that the teeth in both radial sections of an element can be secured to a common boom which, of course, constitutes a D.C. short circuit between sections but does not constitute an R.F. short circuit between sections. Consequently, one radial section can be fed against the other radial section, thus eliminating the necessity for more than two radial sections to constitute an entire operating antenna system.

The above-mentioned and other objects and features of the invention will be more fully understood from the following detailed description thereof when read in conjunction with the drawings in which:

FIG. 1 shows a form of the invention wherein a single antenna element is mounted vertically over ground to produce a vertically polarized unidirectional radiation pattern;

FIG. 2 shows a form of the invention employing a balanced two radial section system mounted above ground and capable of producing either a horizontal or vertically polarized unidirectional pattern, depending upon the orientation of the system;

FIG. 3 shows a form of the invention employing two antenna elements lying in the same plane with their vertices pointing at each other and substantially coincident in space to produce a bidirectional horizontally polarized radiation pattern;

FIG. 3a shows a blown-up View of the vertex of the structure of FIG. 3 and the electrical connections for supplying an input signal thereto;

FIG. 4 shows an antenna system employing four radial sections having a common central support boom and arranged in space quadrature around said boom to produce a circularly or elliptically polarized unidirectional radiation pattern;

FIG. 4a shows a blown-up representation of the vertex of the structure of FIG. 4 and the electrical connections for supplying the input signal thereto;

FIG. 5 shows an adaptation of the invention to an antenna system employing two of the structures shown in FIG. 4, with their vertices pointing at each other and substantially coincident in space, and which is capable of producing a rotating omnidirectional radiation pattern;

FIG. 5a shows a blown-up representation of the vertex of the structure of FIG. 5 and the electrical connections for supplying an input signal thereto; and

FIG. 6 shows another form of the invention employing a single radial section mounted over ground to produce a vertically polarized omnidirectional radiation pattern.

Referring now to FIG. 1, the antenna element is comprised of a number of vertically positioned teeth, such as teeth 29, 21, 22, 23, 24, and 25, which are fastened at their lower end to a ground plane 4th by suitable means not shown in the drawing, but which may be any of several types of conventional fastening means, such as brackets, for example. An alternative method for holding the teeth in a vertical position with respect to the ground plane is by the means of posts and tiewires, which also are not shown in FIG. .1, but which are shown in FIG. 6. The outer ends of the teeth 2% through 25 are defined by the angle 04/ 2 in a well-known manner. The radial dimension of the teeth which are designated by the characters R r R and r have relationships as follows:

Rn 's A coaxial type signal feeding structure designated generally by the reference character 35 is mounted on the teeth 2th through 25 by suitable means such as welding, as denoted by the Weld spots 130, 31, and 132 or by other suitable means, such as brackets of conductive material which are not specifically shown in the drawings. The coaxial feeding means 35 has an inner conductor 34 which forms an angle 5 with the ground plane id measured from the vertex 41. The outer portion of the coaxial feeding means 35 is separated into various segments identified by the reference characters 27, 23$, 29, 3d, 31, and 32, which segments are the portions of the coaxial feeding means which are welded or otherwise supported upon the teeth. The separation in the aforementioned outer section of the coaxial feeding means occurs approximately halfway between adjacent teeth, as shown by typical separations 3-6 and 43. The outer segments of the coaxial feeding means are preferably, although not necessarily, cylindrical in cross section with the inner conductor 34 running continuously through the entire string of segments 27 through 32.

Since the antenna radial section of FIG. 1 is mounted above a ground plane dd, there will be a mirror image thereof reproduced in said ground plane and identified generally by the reference character 42, as shown in the figure. Such mirror image will have the segmented portions corresponding to segments 27 through 32 of the real portion of the antenna. The real radial section and its reflected image will feed against each other to produce a vertically polarized radiation pattern off the vertex l of the system.

It will be noted that the coupling between the inner conductor 34 and the segments 2'7 through 3?. is primarily capacitive in nature. Since the segments 27 through 32 are connected to ground potential through the teeth 2t through 25 upon which they are supported, it might apear that the signal would be short-circuited to ground. However, such is not the case. Although the theory of operation is not fully understood at the present time, it has been found that if the angle 5 is maintained witii a certain range of the order of 3, that there will be no RF. short to ground. To the contrary, substantially all of the energy will be supplied to the teeth 29 through 25 and will be radiated. Although, as indicated above, the theory of this invention is not fully understood, it can be said with a large degree of certainty that the means of coupling the input energy into the antenna system, i.e., the use of the segmented portions 27 tluough 332 and the center conductor 34, functions to load the antenna in such a manner that the phases of the currents in the transverse sections of the teeth Zil through 25 will add together to produce a radiation pattern off the apex 41 of the antenna.

In accordance with embodiments of the invention found suitable, the following ranges of design parameters are applicable:

The angle 5 is varied between 1 and 4 to obtain an optimum standing wave ratio (VSWR), which optimum condition depends upon the values of 06/2 and T. The impedance of the coaxial feeding structure will vary from 50 to ohms, depending again upon the values of 05/ 2, 'r and 5.

Referring now to FIG. 2, there is shown a balanced form of the invention which can be mounted above ground. Such balanced system employs two radial sections 59 and 51, each of which is mounted on a common boom 5'2 which, in turn, may be rigidly secured with respect to a suitable foundation by other mounting means (not shown). Each of the radial sections has six teeth thereon, each tooth supporting one segment of a coaxial feeding means as in the case of FIG. 1. The feed-in coaxial cable 53 is brought in through the rear of the lower coaxial feeding means 54 and carried through to the front of said coaxial feeding means at which point the outer sheath 55 of the feed-in coaxial cable terminates. However, the inner conductor 56 thereof continues out beyond the end of the feeding means 54 and is connected to the inner conductor 57 of the coaxial feeding means 58. Thus, the outer conductor 55 of the input coaxial cable 53 forms the inner conductor for the coaxial feeding means 54 and capacitive coupling occurs between said outer conductor 55 of input coaxial cable 53 and the segmented portion of coaxial feeding means 54. The inner conductor 56, which is connected to the inner conductor 57 of upper coaxial feeding means 53, is capacitively coupled to the segmented portion of the upper coaxial feeding means 53, thus completing the means for feeding the signal to the antenna system. The teeth of the radial sections are connected rigidly and conductively to the individual segments of the feeding means 54 and 53 as discussed in connection with FIG. 1. Also, as in the case of FIG. 1, the angle 5 is of the order 3". With the structure shown in FIG. 2 either a horizontally or vertically polarized radiation pattern can be produced depending upon the orientation of the antenna system. More specifically, if the antenna is oriented in a vertical plane it will produce a vertically polarized unidirectional radiation pattern, and if it is positioned instead in a horizontal plane, it will produce a horizontally polarized unidirectional radiation pattern.

Referring now to the structure of FIG. 3, t 1.61% is shown an embodiment of the invention constructed to produce a bidirectional horizontally polarized radiation pattern. More specifically, the structure of FIG. 3 consists of two of the antenna structures shown in FIG. 2 positioned on a common boom ltlii with their vertices pointed toward each other and substantially coincident. The common boom is mounted on a base 168 by some suitabie means not shown.

The feed-in coaxial cable 167 is brought in from the rear of the coaxial feeding means 193, with the outer sheath 1G5 thereof terminating at the front of the coaxial feeding means 103 but connected by a lead 199 to the inner conductor of coaxial feeding means M1. The inner conductor 1% of coaxial cable 167 is connected to the center conductors of feeding means MP2 and 764. Reference is made to FIG. 3a for a detailed drawing of the connections described immediately above.

Referring now to FIG. 4, there is shown a form of the invention capable of producing a circular or elliptically polarized unidirectional radiation pattern. The structure of FIG. 4 is actually a combination of two of the structures of FIG. 2 positioned on a common boom with a common vertex and with the four radial sections being positioned in space quadrature with respect to each other.

For purposes of discussion, these four radial sections Will be identified by reference characters 50, 61, 62, and 63, with radial sections 60 and 62 lying in the plane of the drawing and radial sections 61 and 63 lying in a plane perpendicular to that of the drawing. The boom 64, which is common to all of said radial sections, forms the main supporting element for the antenna system and can be secured to some suitable base mounted upon the earth. In order to obtain the circularly polarized radiation pattern it is necessary that one of the pairs of radial sections be either stretched or shrunk with respect to the other. Stretching or shrinking a log periodic antenna element involves the lengthening or shortening of all the radial dimensions of that antenna element by a constant factor. For example, if all of the radial dimensions of an antenna element are decreased by a factor of r the phase of the radiated pattern caused by a given input signal will be advanced by 90 with respect to the phase of the radiated signal if said antenna element had not been shrunk. Conversely, if the antenna element were stretched by a factor 'r the phase of the radiated signal will lag by 90 the phase of the radiated signal which would occur in the absence of said stretching.

For a more detailed discussion of the phenomena of the stretching and shrinking, reference is made to the aforementioned United States application Serial No. 841,391.

Returning now to FIG. 4, assume that the radial sections 61 and 63 are shrunk with respect to the radial sections 60 and 62 by a factor K. If I =T1A the time phasing of the signal generated in the radial sections 61 and 63 will lead the signal generated in the radial sections 60 and 62 by 90. Since the two pairs of radial sections are positioned 90 apart in space, the necessary conditions are present for the production of a circular or rotating radiation pattern. For a discussion of other type log periodic antenna structures capable of producing circularly polarized radiation patterns, reference is made to the aforementioned copending application Serial No. 31,068.

As in the case of the structure of FIG. 2 the feed-in coaxial cable 65 is brought in through the rear of one of the coaxial feeding means 66. The said coaxial feed-in cable is brought forward to the front of said coaxial support means 66, at which point the outer sheath is terminated, but a lead is connected therefrom to the inner conductor of coaxial feeding means 73. Reference is made to FIG. 4a which shows an enlarged view of the vertex region of the structure of FIG. 4. The inner conductor 67 of the feed-in coaxial cable is connected to the inner conductor 68 of the coaxial feeding means 70 and also the inner conductor of the coaxial feeding means 69.

As indicated, the above described connections are much more readily discerned from the examination of FIG. 4a which shows the four coaxial feeding means 66, 73, 69, and 70 arranged in quadrature relationship with respect to the central boom 64'. It can be seen that the radial sections 6t) and 63 are energized from the inner conductor 67 of the feed-in coaxial cable 65 and that the radial sections 61 and 62 are energized from the outer sheath '71 of the feed-in coaxial cable 65.

Referring now to FIGS. and 5a, there is shown a form of the invention which is capable of producing a rotating omnidirectional radiation pattern in the XZ plane of FIG. 5. The structure of FIG. 5 consists of two structures similar to that shown on FIG. 4 with the vertiees pointed at each other and with a common boom which extends straight through the center of both the upper half 8t and the lower half 81 of the structure of FIG. 5. The said boom 92 then is mounted on a base 83 by some suitable means not shown. The connections for supplying the input signal to the upper and lower halves of FIG. 5 are made in such a manner that the rotating electric field vector created by each half of the structure of FIG. 5 rotates in the same direction, and coincidentally with each other, in the configuration of l to the structure of FIG. 5 are shown in FIG. 5a.

FIG. 5, thus producing a rotating omnidirectional field of maximum intensity.

The specific connections for supplying the input signal Each of the eight coaxial feeding means of FIG. 5 are identified by the reference characters 8 5 through M, respectively, and are identified in FIG. 511 by the same reference characters, although primed. Similarly, the boom 92 of FIG. 5 is represented by the reference character 92' of FIG. 5a. It will be seen that the feed-in coaxial cable 93 is brought in through the rear of the coaxial feeding means and has its outer sheath terminated at the front of said coaxial feeding means 93*. The inner conductor 95 is carried forward, however, and connects to the inner conductor 98' of feeding means 89 and the inner conductor $9 of feeding means 88 of the lower half of the structure of FIG. 5 and also connects to the inner conductors of feeding means 34- and 85' of the upper half of the structure of FIG. 5. The outer conductor or sheath of the feed-in coaxial cable is connected to the inner conductor of the feeding means 91' of the lower half of FIG. 5 and is also connected to the inner conductors of feeding means 87 and 86 of the upper half of the structure of FIG. 5.

The connections of FIG. 5 cause the rotating fields of the half sections of FIG. 5 to rotate together. Consequently, it is necessary that, separately, the rotating fields should rotate in opposite directions. More specifically, if each of the halves of the antenna structure of FIG. 5 were viewed from the vertex it would be necessary that the field radiated by one of the halves rotate clockwise and that the field produced by the other half of the structure rotate in a counterclockwise direction in order that the two radiated fields should rotate together when the half sections are joined vertex to vertex. The aforementioned objective of coincident rotation can also be obtained by shrinking a pair of the radial sections in a given plane in one half (either upper or lower) of the antenna structure of FIG. 5 by a factor 7 and by stretching the radial sections in the same plane in the other one-half of the antenna structure by a factor Such a procedure will cause rotation of the radiated field on the two half sections in the same direction when joined vertex to vertex. If both stretching and shrinking is done, as indicated in the preceding sentences, the connections to the inner conductors of coaxial support members 85 and 87 of FIG. 5a will have to be reversed. (Assuming that the radial sections comprising the coaxial type feeding means 85', 8'7, 91, and 89 are the ones involved in the shrinking and stretching.)

Referring now to structure of FIG. 6, there is shown still another form of the invention which is mounted directly over a ground plane and produces in said ground plane a reflection thereof, thus completing the antenna structure in a manner similar to that described in connection with the structure of FIG. 1. The real part of the structure is designated generally by the reference character 12d and the reflected radial section is designated generally by reference character 121, and shown in dotted lines. As in the case of FIG. 1, the feed-in coaxial cable 122 preferably, although not necessarily, is brought in underground and the outer sheath 123 thereof terminates at the ground plane 126 with the inner conductor extending upward and being connected to the inner conductor 124 of the coaxial feeding means 125. The feeding means 125 forms an angle .5 with the ground plane 126 measured from the vertex 127 of the antenna. As in the case of FIG. 1, the value of g is approximately 3, although some variation on either side of 3 can be tolerated with suitable results. The amount of variation permissible in all forms of the invention described herein is determined by the quality of performance desired from the structure. The structure of FIG. 6 produces a unidirectional vertically polarized radiation pattern.

The real antenna element of the structure of FIG. 6 is supported by posts 135 and 145, which have a main supporting catenary 137 hung therebetween. From this catenary 137 tiewires, such as tiewires 1 38, 139, 140, and 141, support the individual teeth, such as teeth 14 8, 149, and 150* of the antenna element by means of insulators, such as insulators 14-2, 143, and 144. Guy wires 151 and 152 help support the posts 136 and 145.

It is to be noted that the forms of the invention herein shown and described are but preferred embodiments thereof and that the invention may be inconporated with other log periodic antenna configurations without departing from the spirit or the scope of the invention.

We claim:

1. In a log periodic antenna structure comprising at least a first radial section having a vertex and two sides forming an angle 01/2 extending from said vertex to form a generally triangular shape, said radial section further comprising a supporting means positioned along one of said sides, a plurality of teeth secured to said supporting means and extending outwardly and generally transversally from said supporting means, the outer ends of said teeth being defined by the other side of said angle u/Z, the radial distance from the vertex to a given point of any tooth bearing a relationship 1- to the radial distance to the corresponding point on the next adjacent tooth farther removed from said vertex, a coaxial type signal feeding means comprising a segmented outer conductor extending along a line forming an angle with said vertex and being rigidly and conductively secured to said teeth, the segmented outer conductor of said feeding means being separated near the midpoint of the distance between each pair of adjacent teeth, continuous inner conductor means positioned within said segmented outer conductor, other structure means against which said first radial section can feed, and transmission line means comprising first and second conductor means, said first conductor means being connected to said inner conductor means of said feeding means and said second conductor means being connected to said other structure means.

2. A log periodic structure in accordance with claim 1 in which said transmission line means comprises a coaxial cable having an inner conductor which comprises said first conductor means and having an outer sheath which comprises said second conductor means.

3. A log periodic antenna structure in accordance with claim 2 in which said other structure means comprises a ground plane and in which said radial section is mounted above said ground plane in a plane perpendicular to said ground plane with said supporting means positioned substantially in said ground plane and electrically connected to said ground plane, said feed-in coaxial cable means being brought up near the vertex of said radial section from below said ground plane, and said coaxial cable means having the said outer sheath thereof connected to said ground plane near said vertex.

4. A log periodic antenna structure in accordance with claim 2 in 'which said supporting means comprises a boom and in which said other structure means comprises a second radial section mounted on said boom in the same plane as said first radial section and being positioned to be a mirror image of said first radial section, the said feed-in coaxial cable means being brought in through the said feeding means of said second radial section with the outer sheath of said feed-in coaxial cable means constituting the inner conductor of said second radial section and being capacitively coupled to the segmented outer portion of said second radial section.

5. A log periodic antenna structure in accordance with claim 4 comprising a third radial section and a fourth radial section which are mirror images of said first and second radial sections, respectively, which are secured on opposite sides of a second supporting boom, the said second supporting boom being positioned end to end with said first boom and lying in a straight line therewith, the said third and fourth radial sections being positioned in the same plane as said first and second radial sections with their vertices pointing in opposite directions with respect to the vertices of said first and second radial sections but being positioned substantially coincidental with the vertices of said first and second radial sections, the inner conductor of said fourth radial section being connected to the outer sheath of said feed-in coaxial cable, and the inner conductor of said third radial section being connected to the inner conductor of said feed-in coaxial cable means.

6. A log periodic antenna structure in accordance with claim 4 comprising a third and a fourth radial section similar to said first and second radial section, but with all radial dimensions multiplied by a constant factor 1 said third and fourth radial sections being mounted on said boom but in a plane perpendicular to the plane of said first and second radial sections, the vertices of all four of said radial sections pointing in the same direction and being positioned substantially coincident in space, the said feed-in coaxial cable means having its inner conductor connected to the inner conductor of the feeding means of said third radial section and its outer sheath connected to the inner conductor of the feeding means of said fourth radial section.

7. A log periodic antenna structure in accordance with claim -6 comprising fifth, sixth, seventh, and eighth radial sections which are mirror images of the first, third, second, and fourth radial sections, respectively, and which are mounted in space quadrature on a second supporting boom in the order enumerated with all vertices pointing in the opposite direction of the vertices of said first, third, second, and fourth radial sections and positioned substantially coincidental therewith in space, the fifth and seventh radial sections lying in the same plane as the first and second radial sections and the sixth and eighth radial sections lying in the same plane as the third and fourth radial sections, said feed-in coaxial cable means having its outer sheath connected to the inner conductors of the feeding means of said sixth and seventh radial sections and its inner conductor connected to the inner conductors of the feeding means of said fifth and eighth radial sections.

8. A log periodic antenna structure in accordance with claim 6 comprising fifth, sixth, seventh, and eighth radial sections mounted on a second supporting boom lying in a strai ht line and end to end with the first boom and in the order enumerated, said fifth, sixth, seventh, and eighth radial sections being arranged in space quadrature with each other and with all vertices pointed in a direction opposite the vertices of said first, second, third and fourth radial sections and positioned substantially coincidental therewith in space, said fifth and seventh radial sections lying in the same plane as said first and second radial sections and being mirror images thereof, respectively, said sixth and eighth radial sections being mirror images of each other and being mounted in the same plane as said third and fourth radial sections and with all radial dimensions multiplied by a constant factor of 'rwith respect to the radial dimensions of said first and second radial sections, the said feed-in coaxial cable having its inner conductor connected to the inner conductors of the feeding means of said seventh and eighth radial sections and its outer sheath connected to the inner conductors of the feeding means of said fifth and sixth radial sections.

No references cited. 

1. IN A LOG PERIODIC ANTENNA STRUCTURE COMPRISING AT LEAST A FIRST RADIAL SECTION HAVING A VERTEX AND TWO SIDES FORMING AN ANGLE A/2 EXTENDING FROM SAID VERTEX TO FORM A GENERALLY TRIANGULAR SHAPE, SAID RADIAL SECTION FURTHER COMPRISING A SUPPORTING MEANS POSITIONED ALONG ONE OF SAID SIDES, A PLURALITY OF TEETH SECURED TO SAID SUPPORTING MEANS AND EXTENDING OUTWARDLY AND GENERALLY TRANSVERSALLY FROM SAID SUPPORTING MEANS, THE OUTER ENDS OF SAID TEETH BEING DEFINED BY THE OTHER SIDE OF SAID ANGLE A/2, THE RADIAL DISTANCE FROM THE VERTEX TO A GIVEN POINT OF ANY TOOTH BEARING A RELATIONSHIP T TO THE RADIAL DISTANCE TO THE CORRESPONDING POINT ON THE NEXT ADJACENT TOOTH FARTHER REMOVED FROM SAID VERTEX, A COAXIAL TYPE SIGNAL FEEDING MEANS COMPRISING A SEGMENTED OUTER CONDUCTOR EXTENDING ALONG A LINE FORMING AN ANGLE E WITH SAID VERTEX AND BEING RIGIDLY AND CONDUCTIVELY SECURED TO SAID TEETH, THE SEGMENTED OUTER CONDUCTOR OF SAID FEEDING MEANS BEING SEPARATED NEAR THE MID-POINT OF THE DISTANCE BETWEEN EACH PAIR OF ADJACENT TEETH, CONTINUOUS INNER CONDUCTOR MEANS POSITIONED WITHIN SAID SEGMENTED OUTER CONDUCTOR, OTHER STRUCTURE MEANS AGAINST WHICH SAID FIRST RADIAL SECTION CAN FEED, AND TRANSMISSION LINE MEANS COMPRISING FIRST AND SECOND CONDUCTOR MEANS, SAID FIRST CONDUCTOR MEANS BEING CONNECTED TO SAID INNER CONDUCTOR MEANS OF SAID FEEDING MEANS AND SAID SECOND CONDUCTOR MEANS BEING CONNECTED TO SAID OTHER STRUCTURE MEANS. 